Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L1/00—Compositions of cellulose, modified cellulose or cellulose derivatives
  • C08L1/08—Cellulose derivatives
  • C08L1/10—Esters of organic acids, i.e. acylates
  • C08L1/12—Cellulose acetate
• • D—TEXTILES; PAPER
  • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
  • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
  • D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
  • D04H1/40—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties
  • D04H1/42—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties characterised by the use of certain kinds of fibres insofar as this use has no preponderant influence on the consolidation of the fleece

Definitions

• the invention relates to a sponge cloth made of cellulose and a process for producing same.
• the remaining pressed cake in ground form is treated with carbon disulfide, forming cellulose xanthogenate, which dissolves readily in a NaOH solution, in which it degrades after a period of time with a reduction in average degree of polymerization (DP).
• DP average degree of polymerization
• the DP is reduced from 800-1200 to 200-600.
• the DP is defined as the average number of individual cellulose molecules of which a cellulose polymer chain is composed on the average.
• the alkaline xanthogenate solution is then mixed with pore-forming Glauber's salt, cotton fibers and optionally a coloring pigment and the mixture is stirred or kneaded until all the components are distributed uniformly. Then the mixture is spread on a web by means of a flat device or a roller-like device.
• the web may have a three-dimensional pattern for profiling the surface of the product.
• the mass on the web is guided for a few minutes in an alkaline coagulation bath enriched with Glauber's salt at 100° C.
• the xanthogenate is thermally cleaved and the pore-forming salt is leached out, forming a spongy structure as the sheet product on the web.
• the sheet product is washed in water and brought in contact with a small amount of 1% sulfuric acid solution to reduce the residual levels of organic carbon disulfide and hydrogen sulfide compounds.
• the object of the invention is to provide a sponge cloth and a process for producing same, where the above-mentioned sulfur compounds, in particular carbon disulfide and hydrogen sulfide, are not present in the sponge cloth at all.
• Another object of this invention is to prevent a reduction in average degree of polymerization DP of the cellulose during the production of the sponge cloth, to achieve higher strength values and increase the storage stability of the cellulose derivatives.
• the starting material for production is decrystallized low-substituted (DS 0.2 through 1.5) acetylated cellulose that is soluble in solvents or solvent systems based on dimethyl sulfoxide or dimethylacetamide. For this reason, derivatization with carbon disulfide need no longer be performed to dissolve the cellulose.
• aqueous lye preferably NaOH solution
• aqueous lye preferably NaOH solution
• the lye is preferably used in at least a four-fold excess, based on the dry weight of the starting pulp.
• the period of time can be less than one hour if prior tests have ensured that swelling of the pulp is complete.
• the lye is removed by squeezing to such an extent that the weight of the remaining pressed cake is three times the dry weight of the starting pulp.
• This pressed cake is ground to particle sizes less than 3 mm in diameter by means of a conventional beater mill or shredder mill and loosened in the process.
• the particles are then placed in a stirred vessel, where a five-fold quantity of a liquid agent that has an acetylating action on sodium cellulose, i.e., the particulate material, is poured over the particles, and the mass is stirred for approx. 60 minutes.
• a liquid agent that has an acetylating action on sodium cellulose i.e., the particulate material
• agents examples include acetic anhydride, glacial acetic acid (anhydrous acetic acid) or acetyl chloride.
• the average degree of substitution DS indicates the number of OH groups that are substituted on the average by the average of three hydroxyl groups of the individual cellulose molecule in its polymer chain. This yields a maximum value of 3 and a minimum value of 0 for the DS.
• the excess substitution agent i.e., the liquid phase
• the cellulose derivative mass which is then in substituted form, is washed with water at least three times and then dried to a white powder at an ambient temperature of 100° C.
• the cellulose derivative powder is then dissolved in a solvent or solvent system based on dimethyl sulfoxide or dimethylacetamide at 20° C. to 50° C. to a concentration of 4 to 12 wt %.
• the preferred solvents have proven to be dimethyl sulfoxide (DMSO), DMSO/lithium chloride (chloride content 5 wt %), DMSO/magnesium chloride (chloride content 3 wt %), DMSO/N-methylmorpholine N-oxide or dimethylacetamide/lithium chloride.
• DMSO dimethyl sulfoxide
• DMSO/lithium chloride chloride content 5 wt %)
• DMSO/magnesium chloride chloride content 3 wt %)
• DMSO/N-methylmorpholine N-oxide or dimethylacetamide/lithium chloride DMSO/N-methylmorpholine N-oxide or dimethylacetamide/lithium chloride.
• the inorganic chlorides serve as solubilizers.
• the dimethyl sulfoxide systems in particular have a good dissolving power, can be handled with no problems with regard to occupational safety and can be recovered easily from laboratory wastes.
• anhydrous salt which serves as the pore-forming agent is added to this solution, which is defined as 100 wt %.
• Such salts are known per se; they are soluble in water and weak acids and do not enter into any interaction with the cellulose derivative.
• the solution is mixed with 0.5 to 4 wt % fibers of natural or synthetic origin that are insoluble in the solvent used and optionally with up to 5 wt % conventional dyes, preferably pigment dyes, and foaming substances.
• anhydrous for the pore-forming salts is to be understood in the sense that they contain only bound water of crystallization at room temperature or none at all.
• NaCl which is available very inexpensively.
• the resulting mixture is stirred or kneaded at room temperature until a homogeneous distribution of all components is obtained, which can be observed by the fact that when the dye is added it is distributed uniformly in the mixture. This process is usually concluded after 10 to 30 minutes.
• the mixture is then poured or spread on a movable web, where the thickness of the applied layer is equal to the desired thickness of the sponge cloth to be produced. If it should have a surface structure, the web used will have a corresponding three-dimensional structure on the surface facing the mixture.
• the thickness of the applied layer is preferably a few millimeters up to three centimeters.
• the coated web is passed through a bath of boiling water, where the dwell time in this bath depends on the amount of time required for complete dissolution of the pore-forming salt and for a spongy cohesive sheet to be formed on the web.
• the sheet can easily be lifted away as a raw product and is washed with water until no residues of the solvent system and free coloring agents can be detected. This is followed by drying at 100C to form a finished sponge cloth in a conventional moving or stationary drying apparatus.
• One variant of the process consists of the fact that, after the spongy structure is treated with boiling water on the moving web, during or following the subsequent washing it is treated for one hour in 0.1 to 2N aqueous sodium hydroxide solution at 50° C. while stirring.
• the acetyl groups present in the sponge are thus cleaved back and subjected to ester saponification.
• This process can also take place at room temperature, but the reaction is greatly accelerated at 50° C. and thus is more economical.
• the reaction can be carried out in an open apparatus.
• the pore structure of the cloth is not altered but this measure imparts the valuable property of extremely spontaneous wetting with water.
• an inorganic carbonate or bicarbonate in the amount of 0.1 to 3 wt % may be added as the foaming agent to the mass applied to the web before the treatment in boiling water.
• the boiling water contains an organic or inorganic acid in small quantities that are nevertheless sufficient to completely form carbon dioxide from the carbonate or bicarbonate.
• a pH of 6 or slightly less has proven adequate.
• acids of lower hazard classifications can also be used, such as citric acid.
• Acetic anhydride has proven to be an especially suitable acetylating agent because it is available at a low cost.
• the sponge cloth according to this invention does not contain any organic or inorganic sulfur compounds because sulfur atoms are not necessarily present in the solvent, where they remain chemically inactive.
• the corresponding properties of the end products can be determined in advance through the choice of raw materials with their DP values without having to take into account the DP degradation step which is difficult to control.
• the cellulose derivatives can be stored even for several months in the solvents mentioned above without any change in DP.
• the squeezed pulp is ground and excess acetic anhydride is poured over it in an apparatus equipped with a stirrer and a cooling device and stirred for half an hour.
• the solid mass is filtered out and rewashed with water until the pH of the wash water is neutral.
• the pressed cake is loosened, placed on a tray and dried at 100° C. until reaching a constant weight.
• the DS is determined by saponifying the cellulose acetate with NaOH, titrating the excess NaOH back with HCl, and the DS is calculated from the NaOH consumption. A DS of 0.75 is obtained.
• This solution is transferred to a kneader. Then 16.7 g cotton fibers, 2 kg NaCl and 2 g sodium bicarbonate are added. Next the mixture is kneaded for 30 minutes. The homogeneous mass is spread on a profiled web and leveled out, and a profiled mating web is pressed against it to impart a structure to both sides of the paste. The web is boiled for 10 minutes in a water bath where a pH of 5 has been set with citric acid. The finished sponge cloth can be removed from the web; it separates easily from the web during the boiling process.
• the DP shows according to DIN 54,270 (dissolving the cellulose in iron tartarate solution and determining the specific viscosity with and without cellulose) that any reduction in DP in comparison with the initial state does not exceed the tolerance of the measurement method.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• Health & Medical Sciences (AREA)
• Textile Engineering (AREA)
• Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)
• Chemical Or Physical Treatment Of Fibers (AREA)
• Coloring (AREA)
• Paper (AREA)
• Treatments For Attaching Organic Compounds To Fibrous Goods (AREA)

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Citations (17)

• 1996
  • 1996-06-14 DE DE19623704A patent/DE19623704C1/de not_active Expired - Fee Related
• 1997
  • 1997-06-12 AT AT97109565T patent/ATE197321T1/de not_active IP Right Cessation
  • 1997-06-12 ES ES97109565T patent/ES2152595T3/es not_active Expired - Lifetime
  • 1997-06-12 EP EP97109565A patent/EP0812942B1/de not_active Expired - Lifetime
  • 1997-06-16 US US08/876,573 patent/US5910275A/en not_active Expired - Fee Related
• 1999
  • 1999-01-20 US US09/234,257 patent/US6281259B1/en not_active Expired - Fee Related

Patent Citations (17)

Non-Patent Citations (2)

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